In modern medical practice, various types of radially expandable endoluminal devices, such as stents and stented grafts, are frequently implanted within the lumens of blood vessels or other anatomical conduits. Typically, these endoluminal devices are initially mounted on a pliable delivery catheter while in a radially compact state, and the delivery catheter (having the radially compact endoluminal device mounted thereon) is then transluminally advanced through the vasculature or other system of anatomical passageway(s), to the location where the endoluminal device is to be implanted. Thereafter, the endoluminal device is caused to radially expand to an operative, radially expanded configuration wherein it engages the surrounding wall of the blood vessel or other anatomical conduit, frictionally holding the endoluminal device in its desired position within the body.
Many of the radially expandable endoluminal devices of the prior art have been generally classifiable in one of two (2) categories: i.e., self-expanding or pressure-expandable. Endoluminal devices of the "self-expanding" variety are usually formed of a resilient material (e.g., spring metal) or shape memory alloy, which automatically expands from a radially collapsed configuration to a radially expanded configuration, and are typically mounted on a delivery catheter which incorporates some constraining apparatus (e.g., a retractable restraining member, sheath or wall of the delivery catheter) which operates to hold the device in its radially compact state until it is desired to release the device at its site of implantation.
Endoluminal devices of the "pressure-expandable" variety are typically formed at least partially of malleable or plastically deformable material which will deform as it radially expands, and are initially formed in a radially compact configuration and mounted on a delivery catheter which incorporates a balloon or other pressure-exerting apparatus which serves to pressure-expand the endoluminal device when at its desired implantation site. Typically, when these pressure-expandable endoluminal devices are mounted on a balloon catheter, the balloon is initially deflated and furled, twisted or twined to a small diameter, to allow the radially compact endoluminal device to be mounted thereon. Subsequent inflation of the balloon will then cause the endoluminal device to radially expand, to its radially expanded, operative diameter.
In some procedures, it is important that the endoluminal device be prevented from rotating or undergoing torsional deformation as it is being expanded from its radially compact configuration, to its radially expanded configuration. Such prevention of rotation or torsional deformation is particularly important when precise rotational orientation of the endoluminal device must be maintained.
One example of a procedure wherein precise rotational orientation of an endoluminal device is critical, is the deployment of a modular endoluminal graft within a bifurcated or branched segment of a blood vessel (e.g., within the aorto-iliac bifurcation to treat an infrarenal aortic aneurysm which involves the iliac arteries). In such procedures, a primary graft is initially implanted within one of the involved blood vessels (e.g., within the infrarenal aorta), such than one or more opening(s) formed in the primary graft is/are aligned with the other involved vessel(s) (e.g.,with one or both of the iliac arteries). One or more secondary graft(s) is/are then implanted within the other involved blood vessel(s) (one or both of the iliac arteries) and such secondary graft(s) is/are connected to the corresponding opening(s) formed in the primary graft. Thus, in these "modular" endovascular grafting procedures, it is important that the primary graft be positioned and maintained in a precise, predetermined rotational orientation to ensure that the opening(s) of the primary graft will be properly aligned with the other involved blood vessel(s). Any untoward rotation or torsional deformation of the primary graft during its radial expansion may result in nonalignment of the primary graft's opening(s) with the other involved vessel(s), and could render it difficult or impossible to subsequently connect the secondary graft(s) to the opening(s) in the primary graft, as desired.
Examples of modular endovascular grafts useable for aorto-iliac implantation as summarized above include those described in the following United States patents: U.S. Pat. No. 4,577,631 (Kreamer); U.S. Pat. No. 5,211,658 (Clouse); U.S. Pat. No. 5,219,355 (Parodi et al.); U.S. Pat. No. 5,316,023 (Palmaz et al.); U.S. Pat. No. 5,360,443 (Barone et al.); U.S. Pat. No. 5,425,765 (Tifenbrun et al.); U.S. Pat. No. 5,609,625; (Piplani et al.); U.S. Pat. No. 5,591,229 (Parodi et al.); U.S. Pat. No. 5,578,071 (Parodi); U.S. Pat. No. 5,571,173 (Parodi); U.S. Pat. No. 5,562,728 (Lazarus et al.); U.S. Pat. No. 5,562,726 (Chuter); U.S. Pat. No. 5,562,724 (Vorwerk et al.); U.S. Pat. No. 5,522,880 (Barone et al.); and U.S. Pat. No. 5,507,769 (Marin et al.).
In cases where a pressure-expandable endoluminal device is mounted upon and expanded by a balloon catheter (as described above), any significant rotation or torsional motion of the balloon during inflation, may result in corresponding rotation and/or torsion of the endoluminal device. This is especially true in cases where the balloon is relatively bulky, or of relatively large diameter, such as those balloons used to expand and implant endoluminal devices in large diameter vessels, such as the human aorta. Thus, the usual technique of furling, twining or twisting the deflated balloon prior to mounting of the endoluminal device thereon, may result in untoward rotation of torsional deformation of the expanding endoluminal device as the balloon is inflated.
Accordingly, there exists a need in the art for the development of new methods and/or devices for preventing rotation or torsional deformation of radially expandable endoluminal devices (e.g., stents, stented grafts, etc.) during implantation.